PORTSMOUTH - Workers and patrons evacuated an office building this morning after fears the heavy snow on the roof could cause a collapse, but engineers quickly determined that the building was safe and they were allowed back inside.

Firefighters responded to the Griffin Park Professional Building at 200 Griffin Road just before 9 a.m. to check the safety of the building after occupants noticed a 1-inch gap between the ceiling tiles and sprinkler heads, Fire Capt. Todd Germain said.

Employees feared the ceiling was about to collapse due to the snow load on the roof.

Germain said about 50 employees and other patrons evacuated the building, which houses several business offices, while firefighters investigated. A building engineer who designed the building lives nearby and responded to inspect the building as well.

Germain said the engineer determined that the building was safe because it was designed to “flex” a certain amount and can handle the amount of snow on the roof.

"Essentially the snow load, as heavy as it is, was still well within the safety design of the building," Germain said.

Germain said the roof drains were also checked and were working fine.

"They did the right thing. They saw something that seemed unusual and they knew there was a snow load up there," Germain said.

All of the building's occupants were allowed back inside less than an hour after firefighters arrived. The heavy snow in recent weeks has prompted concerns about roof collapses.

Germain said it’s important that roof drains are clear of ice to allow proper drainage. Officials have also urged people to clear heavy snow loads from flat roofs to avoid a collapse.